The present invention relates generally to drawn and ironed two-piece containers having an end seamed to the open end of the container body. One common use for such containers is as a beverage package. More particularly the present invention relates to light weight containers which require less metal per container and can have a lower cost to produce and higher overall quality when compared to currently produced versions. The lightweight beverage containers of the present invention have one or more of the following features: 1) a reduced seam between the can end and the can body, 2) a side wall having vertically disposed alternating portions of relatively thicker and relatively thinner metal, 3) a can end dimensioned to fit when stacked within the domed bottom of a vertically adjacent similar can, 4) a can body produced from a non-circular blank dimensioned to produce said can body with reduced ears, and 5) a can body produced from a cup having a variable radius between the side of said cup and the bottom thereof.
A typical two piece container consists of a unitary deep drawn body that includes a cylindrical side wall and an integral bottom wall closing one end of the can. Usually the beverage can body has a necked inward throat at its top which terminates in an outwardly extending body curl. An end for the can is provided with an end curl that can interact with the body curl in seaming apparatus to attach the end to the can body after filing of the can to provide the requisite hermetic seal.
It is economically very desirable to form the can bodies and ends from as thin a sheet stock as possible while retaining the necessary performance parameters. Numerous container constructions have been developed in the past. Many of these have been directed toward improving the performance of the beverage container and as a result have allowed a reduction in the metal usage per container. Indeed the average number of 12 ounce beverage containers produced from one pound of metal has increased substantially over the past several years.
A number of methods are known for fabricating the can bodies. In one method, known as the "draw and iron" method, a blank is formed from the stock material. The blank is then formed into a large diameter cup in a ram press. The large diameter cup is then reformed into a cup having essentially the diameter desired for the final can body. The cup is then supported from its interior and one or more ironing rings having inside diameters equal to the desired diameter of the finished can body are passed over the outside of the side wall of the can body. This thins and stretches the metal of the side wall making the can body taller.
Optionally, beverage can bodies are then subjected to an additional forming step to modify the cylindrical shape of the side wall of the can body to create a desirable appearance. Generally this is accomplished by inserting a die or inflatable bladder into the can body and using it to press the side wall of the can body outward into a mating die to form the desired pattern or shape. An exemplary process is described in U.S. Pat. No. 5,533,373. These processes involve extra processing steps, which increase the cost of the cans produced, and are predominately used for aesthetic reasons.
After cupping, drawing and again after ironing the top edge of the can body is uneven because the metal tends to stretch slightly more in the direction of the grain of the metal than across the grain of the metal. This condition is called "earing". A can body exhibiting earing must be trimmed along its top edge to facilitate seaming of the can body to the can end. Earing can be reduced by forming the can body from a non-circular blank as described in U.S. Pat. No. 4,711,611. However, the improved non-circular blanks of the present invention are capable of reducing earing in the cupper even more that those described in the prior art.
The trimmed can body is then seamed to a can end to form a hermetically sealed package for a beverage or other food product. Conventional beverage can ends have a relatively flat central panel with an easy open pull-tab attached thereto. The central panel has a countersunk ridge around the periphery of the central panel and a seaming curl projecting upwardly and outwardly from the countersunk ridge. During seaming the seaming curl is folded together with the top edge of the can body to form a complete hermetic seal between the can body and the can end. Some attempts have been made to reduce the size of the seam with a corresponding reduction in the amount of metal consumed by the container. For example a conventional seam used in an aluminum beverage can has a height of about 0.100 inches and the "microseam" described in U.S. Pat. No. 5,595,322 with respect to steel food cans is only 0.060 inches tall. However, steel food cans have flat ends and typically do not have pull-tabs. Accordingly, steel food can ends are readily stackable prior to seaming to a food can body. On the other hand, any attempt to use a "microseam" from a food can or other reduced height seam in a beverage can end will result in a can end that will not form a stable stack prior to seaming. Accordingly, handling by high speed seaming equipment is impeded and there is a need for a stackable design.